Borro, Girolamo

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(also known as Borri, Girolamo; Borrius, Hieronymus) (b. Arezzo, Italy, 1512; d. Perugia, Italy, 26 August 1592), natural philosophy, medicine,methodology of science. For the original article on Borro see DSB, vol. 15.

After the publication of Charles Schmitt’s article in DSB, scholars have paid very little attention to the figure of Girolamo Borro. Regarded as typical outcomes of the most conformist Aristotelianism, Borro’s works have been scarcely studied in recent years, not least because their prolix (and often boring) prose does not facilitate their reading.

Nevertheless, it would not be without interest to go deeper into Borro’s thought, because he seems to share with other natural philosophers of the Tuscan scene (such as, for instance, Andrea Cesalpino and Francesco Buonamici) a remarkable refusal to resort to occult and theological causes in the explanation of natural phenomena. This genuinely naturalistic approach might have exerted some influence on the young Galileo Galilei, who could also have profited from the notable experimental vein that marked the debate on motion developed by the Pisan professors of philosophy (among which Borro was a prominent figure) at the end of the sixteenth century.

Professor of philosophy at the University of Pisa when Galileo was a student there, Girolomo Borro is the author of several works, including two relevant treatises on natural philosophy—an intriguing dialogue on tides (Dialogo del flusso e reflusso del mare, 1561, with further revised editions printed in 1577 and 1582), and a book on the motion of heavy and light bodies (De motu gravium et levium, 1575). Borro’s works are important for a deeper appreciation of the Renaissance Aristotelian natural philosophy; they also provide valuable clues to reconstruct Galileo’s scientific training. Indeed, the abovementioned books on tides and on motion were both owned by Galileo, who should have read them carefully. Thus, Borro’s theory of tides is discussed in the Fourth Day of the Dialogue concerning the Two Chief World Systems, whereas the De motu gravium et levium is explicitly cited in Galileo’s youthful writings on motion (De motu antiquiora), and proved to be an influential source for a few remarkable aspects of his early dynamics.

Relationship to Aristotle. Born in Arezzo in 1512 and dying in Perugia eighty years after (for his biography see Charles Schmitt’s article in DSB), Borro has been pictured as the typical exponent of the most conservative Aristotelianism. Actually, his allegiance to Aristotle was indefectible: “Aristotle, the true guide of philosophers,”—he wrote in the preface to the De motu gravium et levium— “was given us as a divine gift; the whole posterity learnt more, and in a easier, better and sooner way, from him alone than from all antecedents” (De motu gravium et levium, Florence: Marescotti, 1575, Preface: p. 2n).

Nevertheless, Borro’s Aristotelianism cannot be properly defined scholastic. With the exception of Albertus Magnus and Witelo (cited in his book on tides), Borro did not mention any Christian authors, his sources mostly consisted of Greek and Hellenistic philosophers, and, among the medievals, of Arab thinkers (Averroës, Avicenna, Avempace, and al-Ghazali).

This absence of references to Christian authors was not by chance, as it reflects Borro’s antitheological attitude. The Pisan professor was imprisoned twice by the Roman Inquisition (in 1551 and in 1583), while, in 1567, he was implicated in the third heresy trial of Pietro Carnesecchi. Moreover, like his colleague Buonamici, Borro maintained that God contemplated only himself, without bothering about human matters: “The life of God consists in a perpetual activity of conceiving and loving himself,” he wrote in De motu gravium et levium(1575, p. 59), and in his treatise on tides he explained that God could not turn his mind to inferior entities, because, in doing so, “he would fail in being divine” (Del flusso e reflusso del mare, 1577, p. 56). Hence, the Pisan professor did reject any interference of the divinity in ordinary course of nature, claiming that miracles had to be considered as results of ignorance: “Whoever knows the way by which the nature generates the springs”—he stated in denying that a source in Tuscan countryside could be deemed miraculous because of the great amount of water gushing from it—“can easily understand the cause of the effects produced by that spring” (ibid., p. 240).

Thus, like other exponents of the Tuscan Aristotelianism of the age (Buonamici, Cesalpino, Flaminio Nobili, and Francesco Piccolomini), Borro adopted a resolute naturalistic approach, marked by a drastic refusal to introduce theological arguments within the framework of natural phenomena’s inquiry. According to this approach, always “processes and effects of nature originate from the natural form of their causes” (ibid., p. 42).

Also in explaining sea tides Borro resorted to a natural cause, because he viewed the raising of seas as produced by a rarefaction of waters due to the moonlight’s heat. In fact, “the heat entering humid bodies makes them more rarefied and inflates them … hence, the sea will swell and begin to raise the more the moon will be out from its oblique horizon [i.e., the more the moon will be higher in the sky]” (ibid., pp. 125–126).

In defending such a theory (already held by several authors in Middle Ages), Borro openly rejected the role of astrological influences, strongly denying their existence. According to him, the discovery of the natural cause of a phenomenon “gets rid of influences, and this is especially true in the case of sea tides, in which they do not play (nor they could not play), any part, because they do not exist at all” (ibid., p. 47).

De motu. The most interesting of Borro’s works is perhaps the De motu gravium et levium, published in 1575. The problem of the motion of heavy and light bodies was a very controversial issue among the renaissance Aristotelians. As Borro claimed at the beginning of his book: “There is nothing that philosophers debate as much over, and nearly come to blows over, as this motion [of heavy and light bodies]” (De motu gravium et levium, p. 2).

Even if its pages do not include any explicit reference to such a circumstance, Borro’s book was very likely connected to a quarrel on the matter aroused among Pisan professors. At that time, it was usual for philosophers not to mention their adversaries by name, and this custom may account for the silence kept by Borro on his opponents. Anyway, his main rival in the quarrel should have been his colleague Buonamici, whose De motu, published in 1591, holds views directly opposed to those defended by Borro.

In contrast with Buonamici’s allegiance to Greek Aristotle’s commentators, Borro held a strict Averroist position. In particular, he maintained the typical Averroist thesis that the elements (whose dynamical tendencies determined, according to Aristotelian physics, the motion of terrestrial bodies) were not true substances, but intermediate entities between substance and accident. On this ground, Borro also argued that each element had a peculiar motion, being directly and entirely moved by its form. Borro’s firm Averroist stance was underlined by Galileo (see Opere di Galileo Galilei, Ediz. Naz., I, p. 333), who also remarked that the philosopher from Arezzo treated the subject of motion “most thoroughly” (exactissime; ibid., p. 367).

In his early writings on motion Galileo might have drawn inspiration from Borro’s De motu gravium et levium in order to defend his theory of extrusion as cause of the motion upward. Replying to the objection according to which, if bodies moving upward were truly extruded by the medium, then, because their motion was enforced, they should move more slowly at the end (which did not occur), Galileo claimed that when the mover (motor) is joined (coniunctus) to the body—as in the case of bodies extruded by the medium—it is not necessary for speed to decrease (see ibid., p. 365). The notion of motor coniunctus may have been suggested to Galileo by Borro’s treatment of those natural motions in which the speed of the body increases by virtue of the action of the medium (antiperistaltic acceleration). In these kind of motions, “the mover is always joined [coniunctus] to the body, therefore it always moves and, in moving, acquires a greater power, by which the motion becomes swifter at the end” (De motu gravium et levium, p. 235). According to this explanation, it was thus possible to posit a natural motion in which the medium played an active role. Even if Galileo used the concept of motor coniunctus in a very different context, there are several clues that he took inspiration from Borro’s De motu gravium et levium (see Camerota and Helbing, pp. 346–357).

Experiment. A noteworthy aspect of Borro’s book concerns the report of an experiment of fall. In a chapter of his book, titled “What Themistius Claimed against Aristotle and Averroes Claimed against Themistius on the Weight of Air,” Borro recounted how he and some friends dropped pieces of wood and lead of about the same weight from a high window, in order to settle the question of whom (between Averroës and Themistius) were right (see Schmitt’s article in DSB). Borro’s conclusion emphasized the significance of the test:

Compelled by the results of the experiment, all [those present] came to adhere to our opinion. Therefore, by reason, experiment and authority, it is appropriate to conclude that air has some weight in its own place, so that a piece of wood, which contains a greater part of air than a piece of lead of equal weight, descends more swiftly in air. (De motu gravium et levium, 1575, p. 215)

This experiment paralleled similar ones described by Buonamici and by Galileo. Each of them (Borro, Buonamici, and Galileo) relied heavily on experience, invoking experimental evidence to confirm their views. It seems, therefore, that the Pisan debate on motion of the last decades of the sixteenth century was marked by a strong experimental vein (see Camerota and Helbing, pp. 334–345). Hence, the famous “leaning tower experiment,” allegedly performed by Galileo during his years in Pisa, turns out to be much less imaginative than many historians of science have been willing to acknowledge.



Dialogo del flusso e reflusso del mare d’Alseforo Talascopio. Con un ragionamento di Telifilo Filogenio della perfettione delle donne. Lucca, Italy: Busdragho, 1561. Also available from

De motu gravium et levium. Florence, Italy: Marescotti, 1575 (reprinted 1576). Also available from

Del flusso e reflusso del mare, et dell’inondatione del Nilo. Florence, Italy: Marescotti, 1577 (rev. ed. 1582; reprint 1583). Also available from

De peripatetica docendi atque addiscendi methodo. Florence, Italy: Semartelli, 1584.

Lettere scritte a Pietro Aretino. Edited by Teodorico Landoni. Bologna, Italy: Romagnoli, 1873–1875, vol. 2.1, pp. 182–193. These are several letters to Pietro Aretino.

Multae sunt nostrarum ignorationum causae. Biblioteca Apostolica Vaticana, Ms. Ross. 1009, published in Schmitt, 1976 (see below).

Vita magni Cosmi Medicis Etruscorum imperatoris invictissimi. Florence, Italy: Biblioteca Nazionale Centrale. Ms. II. IV. 15, published in Menchini, 2005 (see below).

De constructione syllogismorum. Dedicated to Iacopo Salviati Florence, Italy: Biblioteca Nazionale Centrale, Magl. V. 24, ff. 1r–9r.

Preface to the De motu gravium et levium. Not published because of the death of the recipient of the dedication, the Grand Duke Cosimo I (died in April 1574). Florence, Italy: Biblioteca Nazionale Centrale, Magl. XI. 9, ff. 1r–5r.

Letters to Lorenzo Giacomini Tebalducci, Florence, Italy: Biblioteca Riccardiana, Ms. 2438.

Letters, Siena, Biblioteca Comunale, Ms. D. V. 12. Multae sunt nostrarum ignorationum causae. Biblioteca Apostolica Vaticana, Ross. 1009, ff. 20r–25r (published in Schmitt, 1976).

Vita magni Cosmi Medicis Etruscorum imperatoris invictissimi. Florence, Italy: Biblioteca Nazionale Centrale 2,4,15 (published in Menchini, 2005).


Camerota, Michele, and Mario Helbing. “Galileo and Pisan Aristotelianism. Galileo’s De motu antiquiora and the Quaestiones de motu elementorum of the Pisan Professors.” Early Science and Medicine 5 (2000): 319–365.

Conti, Lino. “Girolamo Borro: cardiocentrismo e ‘perfettione delle donne.’” In Medicina e biologia nella rivoluzione scientifica, edited by Lino Conti, 65–106. Assisi, Italy: Porziuncola, 1990.

Cox, Virginia. “The Single Self: Feminist Thought and the Marriage Market in Early Modern Venice.” Renaissance Quarterly 48 (1995): 513–581. On page 518 is a brief comment on Borro’s dialogue on “women’s perfection” (Della perfetione delle donne), enclosed in the 1561 edition of his Del flusso e reflusso del mare.

De Pace, Anna. “Galileo lettore di Girolamo Borri nel De motu.” In De motu. Studi di storia del pensiero su Galileo, Hegel, Huygens e Gilbert. Milan, Italy: Cisalpino, 1990, 3–69.

Galluzzi, Paolo. Momento. Studi galileiani. Rome: Edizioni dell’Ateneo & Bizzarri, 1979, 113–114, 147, 169, 178. Helbing, Mario Otto. La filosofia di Francesco Buonamici. Pisa, Italy: Nistri-Lischi, 1989.

Ioffrida, Manlio. La filosofia e la medicina (1543–1737). In Storia dell’Università di Pisa, vol. I.1: 239–338 (296–301). Pisa, Italy: Pacini, 1993.

Malpezzi Price, Paola. Moderata Fonte: Women and Life inSixteenth-Century Venice. Madison, NJ: Fairleigh Dickinson University Press, 2003, 128–131. On Borro’s dialogue on “women’s perfection” (Della perfetione delle donne).

Menchini, Carmen. Panegirici e vite di Cosimo I de’ Medici: tra storia e propaganda. Florence, Italy: Olschki, 2005.

Schmitt, Charles B. “Girolamo Borro’s ‘Multae sunt nostrarum ignorationum causae’ (Ms. Vat. Ross. 1009).” In Philosophy and Humanism. Renaissance Essays in Honor of Paul Oskar Kristeller, edited by Edward P. Mahoney, 462–476. Leiden, Netherlands: Brill, 1976.

Schmitt, Charles B. and Quentin Skinner, eds. The CambridgeHistory of Renaissance Philosophy. Cambridge, U.K.: Cambridge University Press, pp. 205, 218, 222, 223, 810.

Settle, Thomas B. “Galileo and Early Experimentation.” In S prings of Scientific Creativity: Essays on Founders of Modern Science. edited by Rutherford Aris, H. Ted Davis, and Roger H. Stuewer, 3–20. Minneapolis: University of Minnesota Press, 1983.

Thurot, Charles. “Recherches historiques sur le principe d’Archimède.” Revue archéologique (1869): 284–299 (295–297). The first source that mentioned Borro’s experiment on fall, with a French translation of the passage from the De motu gravium et levium.

Michele Camerota